1. Field of the Invention
This invention relates broadly to an induction heater introducible into a mammalian body and methods of activating medical implants. More particularly, this invention relates to devices and methods for applying energy to a shape memory medical implant to heat the medical implant to a transition temperature so as to cause the implant to assume an altered configuration.
2. State of the Art
It is known to manufacture medical implants for various applications from a shape memory metal alloy such as Nitinol. When a shape memory medical implant is heated above a phase transformation temperature, a change from the martensitic crystalline structure to the austenitic crystalline structure is induced to cause the implant to revert to a shape that has been heat-trained in the implant during the manufacturing process.
In one specific example, it is known to manufacture otological prostheses from shape memory nickel titanium alloy, and use the shape memory property to cause the implant, upon heating to the phase transformation temperature, to assume an implanted configuration in which a portion of the implant bends and engages an ossicular structure to secure the implant within the ossicular chain. Various devices and methods are known for heating shape memory prosthesis for the middle ear ossicles.
For example, U.S. Pat. No. 6,554,861 to Knox discloses the use of a laser device to generate a laser beam which is directed at a portion of a stapedial prosthesis to cause a bight portion of the prosthesis to bend about an incus to anchor the prosthesis in place. However, the laser must be used with high accuracy and with caution, because if the high energy beam is misdirected off the prosthesis and onto tissue, severe damage to the tissue can occur.
It is also known to use an electrocautery probe to heat a shape memory ossicular prosthesis via conduction across an air gap. However, because the high heat generated by a cautery probe is non-directional, it can also cause collateral damage to surrounding tissue.